Harvard Health Publications

Taking aspirin linked to lower risk of colorectal cancer

Posted By Howard LeWine, M.D. On July 16, 2013

Aspirin has many uses, from easing a headache or cooling a fever to preventing heart attacks and the most common kind of stroke. It may be time to add “preventing colorectal cancer” to the list.

New results from the Women’s Health Study, a clinical trial that evaluated the benefits and risks of low-dose aspirin and vitamin E among nearly 40,000 women, show that aspirin reduces the risk of developing colorectal cancer by 20%. The effect isn’t immediate, but instead takes ten to 20 years to be seen. The findings appear in this week’s Annals of Internal Medicine.

Several earlier studies have linked aspirin use to protection against colorectal cancer. But they were observational studies, which can’t prove cause and effect. The Women’s Health Study was a randomized trial, the gold standard of medical research. As part of the trial, half of the women took 100 milligrams of aspirin every other day and the other half took a placebo every other day. Neither the women, their doctors, nor the researchers knew who was taking what.

The trial began in 1993 and ended in 2004. The initial results showed that aspirin reduced the risk of stroke and also reduced the risk of heart attack among women over age 65, while vitamin E had no effect on heart attack, stroke, or cancer.

After the study ended, the researchers continued to follow more than 33,000 women through March 2012. These women were asked to continue the regimen, although the researchers no longer provided the pills. It was among this group that the researchers saw a 20% lower rate of colorectal cancer.

Interestingly, the researchers saw no difference in colorectal polyps between groups. Polyps are small growths in the wall of the colon or rectum. Some are harmless, some progress to cancer. The new results suggest that aspirin doesn’t prevent polyps from forming, but instead may prevent them from becoming cancerous.

Aspirin isn’t without its drawbacks, including gastrointestinal bleeding and ulcer formation. Both occurred slightly more often among women taking aspirin:

  • gastrointestinal bleeding: 8.3% in the aspirin group, 7.3% in the placebo group
  • ulcer formation: 7.3%in the aspirin group, 6.2% in the placebo group.

Although this study included only women, the results probably apply to men, too. Other studies demonstrating a connection between taking aspirin and protection against colorectal cancer have mainly included men.

Balancing act

Although the Women’s Health Study results sound promising, don’t go reaching for the aspirin bottle just yet. Taking aspirin—and any other drug—is really a balancing act between benefits and risks.

According to the American Cancer Society, this year more than 140,000 Americans will be diagnosed with colon or rectal cancer, and nearly 60,000 people will die from them. Taking a daily low-dose aspirin (81 milligrams) may be one way to help keep you from being included in those statistics.

Aspirin is also a proven strategy for preventing heart attacks and the most common kind of stroke among people who have heart disease or are at high risk for it. In them, aspirin may do double duty.

Yet the risks of aspirin are also very real. Even if aspirin causes an one extra case of gastrointestinal bleeding and one extra ulcer per 100 people (the excess seen in the Women’s Health Study), that translates into more than one million extra cases.

Colorectal cancer doesn’t strike randomly. Some people are at higher risk for it than others, because it runs in their families, they have had colon polyps, or they have ulcerative colitis or Crohn’s disease. And not all colorectal cancers are the same. Some can be turned off by aspirin, others aren’t affected by it.

So it’s still too soon to recommend that everyone take low-dose aspirin to prevent colorectal cancer. If your risk of colon cancer is higher than average, though, it may be worth talking with your doctor about the benefits and risks of taking aspirin.

Beyond aspirin

Keep in mind that there are other ways you can help prevent colorectal cancer:

  • Get screened with colonoscopy once every 10 years to look for polyps and have them removed.
  • Stay physically active and dedicate time to exercise each day.
  • Don’t smoke. Use alcohol in moderation or not at all.
  • Maintain a healthy body weight.

Although not proven, some other steps may help reduce your colorectal cancer risk. Here’s what else you can do:

  • Eat a diet rich in fruits and vegetables.
  • Get enough vitamin D through sunlight, diet and/or pills.
  • Choose whole grain products that provide more fiber.

In the future, it may be possible to better assess an individual’s colon cancer risk and whether prevention with aspirin makes sense. Until then, smarter lifestyle choices—which will have benefits far beyond reducing colorectal cancer risk—make more sense for most people.

Related Information: Living Better, Living Longer: The secrets of healthy aging

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